Chemistry teaches us that heat (in most cases) speeds up chemical reactions, so that is a possibility. On the other hand, the oxidisation of iron is exothermic, so excess heating would slow the rate of rusting. I would guess that the speed of rusting against heat is probably a parabola, so there must be a temperature at which the reaction of iron with air to form iron oxide is capped. I don't know this temperature, but I am fairly sure that it is higher than the temperatures your barbecue will be at. So the barbecue will probably rust faster at the higher temperature.

Hopelessly too vague for any unqualified answer.

Does "scalding" mean 100° or 500°? Does "rusting" mean corroding, or producing rust?

Genuine red rust is mainly hydrated ferric oxide. You might get some at boiling temperatures, but not at temperatures attainable in a brisk barbie fire. However, salt, cresols, carbon black, and a job lot of chemicals encrust barbecues, and many of those strongly encourage rusting at normal temperatures when moist, as anyone can tell by inspecting the typical weathered barbecue.

In fact, contact with rust itself catalytically encourages further rusting because ferric oxide in contact with moist iron forms an electrochemical cell that produces incompletely oxidised iron. Atmospheric oxygen then re-oxidises the lot.

However, if you keep your iron good and hot, say 200° to 400°, in a spray of moisture, you might not get much rust, but you could easily get oxide layers that continually flake off and expose hot iron. Water and air then can attack that exposed iron directly, causing very rapid corrosion indeed, much faster than any of the usual corrosion at comfortable temperatures. So anyone wishing to win bets on this argument, had better keep a tame lawyer and an appropriate chemistry textbook handy.

Cheers,

Jon

Having recently lived in both the Caribbean and Canada, I can assure you that barbecues rust much quicker in a warm climate.

A hot one. Roughly, a 10C rise in temperature doubles the rate of a simple, single-stage reaction like rusting.  That's why exhaust manifolds and mufflers rust faster than steel car body parts.  We live on the temperate south coast of NZ.  When we lived in the tropical Seychelles, where rainfall was about the same as here, cars rusted much faster than here.

The reaction of Iron (FE) with Oxygen (O) to make Iron-Oxide is endothermic (gives out energy) and therefore the colder Barbeque would rust faster.

Infact, under certain temperature and pressure conditions it could be possible for the BBQ to unrust - sounds crazy but can be done.

Jaydaman